The present invention relates to a board on which an electronic part is mounted and a method of mounting the same.
Conventionally, to mount a semiconductor chip (or a BOA (Ball Grid Array)) on a board, solder bumps 102 are respectively formed on pads 101 on a board 100, as shown in FIG. 4A. A flux 103 is applied to the board 100, as shown in FIG. 4B. A semiconductor chip (or BGA) 104 is mounted on the board 100, as shown in FIG. 4C. The semiconductor chip (or BOA) and the board 100 are soldered by a reflow, as shown in FIG. D.
Reference 1 (Japanese Patent Laid-Open No. 57-210638) discloses another conventional mounting method. As shown in FIG. 5, according to this mounting method, to perform soldering by a reflow, a frame-like flow preventing member (dam) 204 is formed to prevent solder bumps 202 from flowing outside corresponding pads 201. Referring to FIG. 5, reference numeral 200 denotes a board; and 203, a semiconductor chip.
Reference 2 (Japanese Patent Laid-Open No. 7-015122) discloses still another conventional mounting method. As shown in FIG. 6, according to this mounting method, a cream solder is filled to form cream solder portions 305 in corresponding openings of a film having electrical insulation and heat resistance properties to prepare a bonding film assembly 304. The bonding film assembly 304 is fed onto a board 300 to overlap the cream solder portions 305 on corresponding pads 301 of the board 300. An electronic part 302 is fed onto the film assembly 304 to overlap leads 303 of the electronic part 302 onto the corresponding cream solder portions 305. The board 300 is heated to melt the cream solder portions 305. As described above, the film assembly 304 prevents the overflow of the cream solder portions 305.
According to the conventional mounting method shown in FIGS. 4A to 4D, a soldering failure such as a solder short 105 and a solder wetting failure 106 may occur in the step shown in FIG. 4D, thereby posing a problem.
The mounting method disclosed in reference 1 can prevent the solder bump flow outside the corresponding pad. However, like in FIGS. 4A to 4D, soldering failures cannot be prevented.
The mounting method disclosed in reference 2, to mount a bare chip with a small pitch, the paste flowing from the film shorts, resulting in a soldering failure.